Intragenomic Polymorphism of the ITS 1 Region of 35S rRNA Gene in the Group of Grasses with Two-Chromosome Species: Different Genome Composition in Closely Related Zingeria Species

Abstract

Zingeria (Poaceae) is a small genus that includes Z. biebersteiniana, a diploid species with the lowest chromosome number known in plants (2n = 4) as well as hexaploid Z. kochii and tetraploid Z. pisidica, and/or Z. trichopoda species. The relationship between these species and the other low-chromosomes species Colpodium versicolor are unclear. To explore the intragenomic polymorphism and genome composition of these species we examined the sequences of the internal transcribed spacer 1 of the 35S rRNA gene via NGS approach. Our study revealed six groups of ribotypes in Zingeria species. Their distribution confirmed the allopolyploid nature of Z. kochii, whose probable ancestors were Colpodium versicolor and Z. pisidica. Z. pisidica has 98% of rDNA characteristic only for this species, and about 0.3% of rDNA related to that of Z. biebersteiniana. We assume that hexaploid Z. kochii is either an old allopolyploid or a homodiploid that has lost most of the rRNA genes obtained from Z. biebersteiniana. In Z. trichopoda about 81% of rDNA is related to rDNA of Z. biebersteiniana and 19% of rDNA is derived from Poa diaphora sensu lato. The composition of the ribotypes of the two plants determined by a taxonomy specialist as Z. pisidica and Z. trichopoda is very different. Two singleton species are proposed on this base with ribotypes as discriminative characters. So, in all four studied Zingeria species, even if the morphological difference among the studied species was modest, the genomic constitution was significantly different, which suggests that these are allopolyploids that obtained genomes from different ancestors.